The present invention relates to battery charger circuits and, more specifically, to a battery voltage regulator for regulating the voltage across each of a plurality of series connected charging batteries.
In order to obtain optimum life from lead-acid batteries, the batteries must be correctly charged. When one charger is used to charge a string of batteries in series, it is unlikely that all of that batteries will receive proper charging, even if all of the batteries are brand new. As a result, some batteries may receive insufficient charge while other receive excess charge. Both of these conditions cause the premature failure of the batteries.
Typically, in series battery string applications, the charger monitors total string voltage rather than individual battery voltages. Since the total string voltage is the sum of the ideal individual battery charging voltages, one battery may receive insufficient charge while another is overcharged. Both overcharging and undercharging, caused by high and low float voltages respectively, damage the batteries and decrease the battery""s life. Overcharging produces excessive heat that can cause the battery plates within the cells to buckle and shed their active material. Undercharging causes unwanted chemicals to build up on the battery plates, reducing its capacity and effective life. Unlike NiCad batteries, lead-acid batteries require constant charging with a float voltage level specified by the manufacturer. To prevent the damage to the batteries, battery manufacturers typically recommend a charging voltage of 13.25 to 13.65 Volts at 25xc2x0 C. However, except in the case of single-battery applications, this recommendation is rarely observed. To complicate matters, the requirements for a given battery also vary with temperature. For example, MK batteries recommends xe2x88x9216.2 mV adjustment to the float voltage for one xc2x0C. temperature change.
In a conventional battery charging circuit, a battery charger may be connected in series with a plurality of batteries. For example, consider three batteries, battery A, battery B, and battery C connected in series with a battery charger. In this example, a 41.1 V battery charger is intended to provide a float voltage of 13.7 V on each battery A, B, and C. When the charging cycle starts, a charge current is supplied to all of the discharged batteries in series. In constant voltage charging, the total string voltage is monitored to determine if all of the batteries have reached the required float voltage. In this example, the required float voltage for each battery is 13.7 V. The charging circuit will operate in float mode when total battery sting voltage is 41.1 V (3*13.7V). If the batteries have uneven float voltages, as is nearly always the case, then the batteries will not receive the proper charge. For example, battery A may have a float voltage of 13.9 V while battery B has a float voltage of 13.5 V, and battery C has a float voltage of 13.7 V. The total string voltage is still 41.1V, but only battery C is being properly charged. In this example, battery A is being overcharged and battery B is not receiving adequate charge. Overcharging produces excessive heat which can damage the battery. Undercharging causes unwanted chemical buildup. Both of these problems reduce the life of the battery. These problems are inherent to all chargers that do not monitor individual battery voltages.
Therefore, there is a need in the art for a system and a method for regulating the float voltage on each of a plurality of batteries during charging.
Additionally, there is a need in the art for a system and a method for compensating for temperature variations in charging batteries during charging.
An object of the present invention is to provide a system and method for regulating the float voltage on a plurality of batteries during charging.
Another object of the present invention is to provide a system and method for providing temperature compensation to charging batteries during charging.
The present invention overcomes the above-described problems in the prior art by providing a system and method for regulating the float voltage on each of a plurality of batteries during charging.
The present invention provides a system and method for charging series connected batteries. The system of the present invention includes a battery charger and a plurality of series connected batteries. Each of the plurality of series connected batteries is connected in parallel with a battery voltage regulation circuit. Each battery voltage regulation circuit comprises a temperature sense circuit, a voltage sense circuit, a reference voltage circuit, a voltage/temperature compensation combiner, and a battery bypass circuit. In addition to being used in conjunction with a plurality of series connected batteries, the present invention may be used with a single charging battery to achieve the same results. Such an implementation of the present invention may be used with a battery charger that is not able to accurately charge a single battery.
The temperature sense circuit receives a parameter correlated to the temperature of a battery and provides a voltage temperature compensation factor correlated to the parameter. The voltage sense circuit receives a parameter correlated to the voltage of a battery. The reference voltage circuit provides a reference voltage associated with a battery. The voltage/temperature compensation combiner receives the voltage temperature compensation factor. The voltage temperature compensation factor is correlated to the voltage of the battery and the reference voltage. The voltage/temperature compensation combiner utilizes the voltage temperature compensation factor and compares the reference voltage of the battery to the parameter correlated to the voltage of the battery to identify excess battery current. The battery bypass circuit provides a current path for removing excess current from the battery path.
Other objects, features, and advantages of the present invention will become apparent upon reading the following detailed description of the embodiments of the invention, when taken in conjunction with the accompanying drawings and appended claims.